Amps are amps...right?

The ampere rating is based on melting element inside the fuse case and the connecting tabs. Fuse case is plastic and has no bearing ion rating.

The smaller holder is maxxed at 30 amps
The next bigger is maxxed at 40 amps, and the bigger is maxed at 50-60 amp.
So whats the question again ??

The difference in physical sizes is so you can use larger wires and connections at the fuse holder itself.

Watts are watts, Amps are amps, Voltage is a variable

Physical size is just a mechanical thing for fitment and connection to the holder and wire.

Electrically fuses are rated in Amps, DC or AC, voltage, and an amps interrupt rating. Also have a rating based on speed to open based on the level of overload ie. slow blow or fast.

For most small 12v stuff it is all about the same. Get the correct amp rating for what fits the holder.

Fuse melting is dependent on WATTAGE. Therefore fuses have voltage ranges in which stated amperage is valid. So in the case of a fuse, an amp is only an amp if the correct voltage fuse is used in the application. Easy to verify, just type in the fuse number on Google, and read what pops up.

I never thought of it that way before, but now I wonder why I have to have three different sizes of U shaped fuses in my vehicles.
bumpy

I pose a question:

Is it perhaps the reaction time of the fuse? Fast blow? Normal? Slow Blow?

MEXICOWANDERER wrote:
Fuse melting is dependent on WATTAGE. Therefore fuses have voltage ranges in which stated amperage is valid. So in the case of a fuse, an amp is only an amp if the correct voltage fuse is used in the application. Easy to verify, just type in the fuse number on Google, and read what pops up.

Fuses are dependent on the current going through them, not the watts. The voltage ratings are based on the physical characteristics - insulation used, the air gap between terminals, the interrupt capability, etc. And, it's not a range, it's a maximum. As Littelfuse says, "a fuse may be used at any voltage that is less than its voltage rating without detriment to its fusing characteristics."

One might say they blow based on wattage in only a very limited sense - they appear in circuit as low resistance resistors, and the current going through them produces power (watts) which heats them up and melts the link, according to I^2 * R. But that's the wattage within the fuse itself, not the number of watts in the circuit being fused.

Please elucidate me as to the relevance of circuit capacity with regards to thermal/wattage issues? Next demonstration. Grab a handful of AGC 30 fuses. Impress 40 amps at 6V across one. Then 35 amps at 36 volts? OOoooo the 35 amps at 36 volts blows the fuse but how about the 6 volt fuse? This is why fuse sizing is an engineering art and not merely rough amperage.

Actual testing and experience with fuse ratings and action reveals some eye-openers. It is very true that lower voltage fuses are not as sensitive thus have a broader tolerance percentage compared to >50 volt devices. But then again many low voltage electronic devices tolerate a operation tolerance range from 10 to 15 volts. Not as many electronic devices operate well ranging 100 - 150 volts.